Self-Standing Lignin-Containing Willow Bark Nanocellulose Films for Oxygen Blocking and UV Shielding

Developing the bio-based barrier material to substitute the petroleum-based one is the trend in functional packaging applications. Utilization of the abundantly underappreciated bark biomass is attractive from the sustainability point of view; however, an upgraded approach is required to maximize the performances of the lignin-containing cellulose nanofibril (LCNF) films from willow bark. Herein, hot water extraction (HWE) and microfluidization were studied for their effect on the yield of LCNF and its film performance after treatment of aqueous p-toluenesulfonic acid. The resultant HWE films were superior to the nontreated ones regarding yield, moisture, and oxygen barrier properties. In particular, the HWE films achieved an oxygen permeability of 3 cm3·μm/m2·kPa·day at 50% relative humidity, which is among the lowest achieved for single bio-based materials and comparable to commercially available synthetic barrier films. The LCNF films attained complete blocking of UV light transmission within the wavelength range of 290-400 nm. Overall, this study shows that HWE pretreatment not only allows the recovery of high-value extracts, but also significantly improves the yield of LCNF and its barrier performances. The biocompatible, lignin-containing, and self-standing hydrophobic nanocellulose films show promise as a barrier layer against UV radiation and oxygen permeation in food packaging and other applications.